Electrochemical sensor and method for manufacturing

ABSTRACT

The present disclosure relates to a sensor including an elongated member including at least a portion that is electrically conductive. The elongated member includes a sensing layer adapted to react with a material desired to be sensed. An insulating layer surrounds the elongated member. The insulating layer defines at least one access opening for allowing the material desired to be sensed to enter an interior region defined between the elongated member and the insulating layer. The insulating layer has an inner transverse cross-sectional profile that is different from an outer transverse cross-sectional profile of the elongated member. The difference in transverse cross-sectional profiles between the elongated member and the insulating layer provides channels at the interior region defined between the insulating layer and the elongated member. The channels extend generally along the length of the elongated member and are sized to allow the material desired to be sensed to move along the length of the sensor.

This application is being filed on 28 Aug. 2008, as a PCT InternationalPatent application in the name of Pepex Biomedical, LLC a U.S. nationalcorporation, applicant for the designation of all countries except theUS, and James L. Say, a citizen of the U.S., applicant for thedesignation of the US only, and claims priority to U.S. Provisionalpatent application Ser. No. 60/969,034, filed Aug. 30, 2007.

TECHNICAL FIELD

The present disclosure relates to sensors for measuring bioanalytes andto methods for making such sensors.

BACKGROUND

Electrochemical bio-sensors have been developed for detecting analyteconcentrations in a given fluid sample. For example, U.S. Pat. Nos.5,264,105; 5,356,786; 5,262,035; 5,320,725; and 6,464,849, which arehereby incorporated by reference in their entireties, disclose wiredenzyme sensors for detecting analytes such as lactate or glucose.Technology adapted for enhancing sensor miniaturization and durabilityis desirable.

SUMMARY

One aspect of the present disclosure relates to an electrochemicalsensor including a sensing layer provided on an at least partiallyconductive fiber having a non-circular transverse cross-sectionalprofile.

Another aspect of the present disclosure relates to a sensor includingan elongated member including at least a portion that is electricallyconductive. The elongated member including a sensing layer adapted toreact with a material desired to be sensed. An insulating layersurrounds the elongated member. The insulating layer defines at leastone access opening for allowing the material desired to be sensed toenter an interior region defined between the elongated member and theinsulating layer. The insulating layer has an inner transversecross-sectional profile that is different from an outer transversecross-sectional profile of the elongated member. The difference intransverse cross-sectional profiles between the elongated member and theinsulating layer provides channels at the interior region definedbetween the insulating layer and the elongated member. The channelsextend generally along the length of the elongated member and are sizedto allow the material desired to be sensed to move along the length ofthe sensor.

A variety of additional inventive aspects will be set forth in thedescription that follows. The inventive aspects can relate to individualfeatures and to combinations of features. It is to be understood thatboth the foregoing general description and the following detaileddescription are exemplary and explanatory only and are not restrictiveof the broad inventive concepts upon which the embodiments disclosedherein are based.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing a sensing tip of a first sensorhaving features that are examples of inventive aspects in accordancewith the principles of the present disclosure;

FIG. 2 is an end view showing the sensing tip of the sensor of FIG. 1;

FIG. 3 is a cross-sectional view taken along section-line 3-3 of FIG. 2;

FIG. 4 is a transverse cross-sectional view of a fiber used within thesensor of FIG. 1, the fiber is shown covered with a layer of sensingchemistry;

FIG. 5 is a schematic view of a sensor system incorporating the sensorof FIG. 1;

FIG. 6 is an end view showing the sensing tip of a second sensor havingfeatures that are examples of inventive aspects in accordance with theprinciples of the present disclosure;

FIG. 7 is a cross-sectional view taken along section line 7-7 of FIG. 6;

FIG. 8 is a schematic view of a sensor system incorporating the sensorof FIG. 6;

FIG. 9 is an end view showing the sensing tip of a third sensor havingfeatures that are examples of inventive aspects in accordance with theprinciples of the present disclosure;

FIG. 10 is a cross-sectional view taken along section-line 10-10 of FIG.9;

FIG. 11 is a cross-sectional view taken along section line 11-11 of FIG.10;

FIG. 12 is an end view showing the sensing tip of a fourth sensor havingfeatures that are examples of inventive aspects in accordance with theprinciples of the present disclosure;

FIG. 13 is a cross-sectional view taken along section-line 13-13 of FIG.12;

FIG. 14 is a cross-sectional view taken along section line 14-14 of FIG.13;

FIG. 15 shows a fifth sensor having features that are examples ofinventive aspects in accordance with the principles of the presentdisclosure, the sensor is shown in cross-section along a section linethat bisects a length of the sensor;

FIG. 16 is a cross-sectional view taken along section line 16-16 of FIG.15;

FIG. 17 is a cross-sectional view taken along section line 17-17 of FIG.15; and

FIG. 18 shows a sixth sensor having features that are examples ofinventive aspects in accordance with the principles of the presentdisclosure, the sensor is shown in cross-section along a section linethat is transverse with respect to the length of the sensor.

DETAILED DESCRIPTION

Reference will now be made in detail to exemplary aspects of the presentdisclosure which are illustrated in the accompanying drawings. Whereverpossible, the same reference numbers will be used throughout thedrawings to refer to the same or like parts.

The following definitions are provided for terms used herein:

A “working electrode” is an electrode at which the analyte (or a secondcompound whose level depends on the level of the analyte) iselectrooxidized or electroreduced with or without the agency of anelectron transfer agent.

A “reference electrode” is an electrode used in measuring the potentialof the working electrode. The reference electrode should have agenerally constant electrochemical potential as long as no current flowsthrough it. As used herein, the term “reference electrode” includespseudo-reference electrodes. In the context of the disclosure, the term“reference electrode” can include reference electrodes which alsofunction as counter electrodes (i.e., a counter/reference electrode).

A “counter electrode” refers to an electrode paired with a workingelectrode to form an electrochemical cell. In use, electrical currentpasses through the working and counter electrodes. The electricalcurrent passing through the counter electrode is equal in magnitude andopposite in sign to the current passing through the working electrode.In the context of the disclosure, the term “counter electrode” caninclude counter electrodes which also function as reference electrodes(i.e., a counter/reference electrode).

A “counter/reference electrode” is an electrode that functions as both acounter electrode and a reference electrode.

An “electrochemical sensing system” is a system configured to detect thepresence and/or measure the level of an analyte in a sample viaelectrochemical oxidation and reduction reactions on the sensor. Thesereactions are transduced to an electrical signal that can be correlatedto an amount, concentration, or level of an analyte in the sample.Further details about electrochemical sensing systems, workingelectrodes, counter electrodes and reference electrodes can be found atU.S. Pat. No. 6,560,471, that is hereby incorporated by reference in itsentirety.

“Electrolysis” is the electrooxidation or electroreduction of a compoundeither directly at an electrode or via one or more electron transferagents.

An “electron transfer agent” is a compound that carries electronsbetween the analyte and the working electrode, either directly, or incooperation with other electron transfer agents. One example of anelectron transfer agent is a redox mediator.

A “sensing layer” is a component of the sensor which includesconstituents that facilitate the electrolysis of the analyte. Thesensing layer may include constituents such as an electron transferagent, a catalyst which catalyzes a reaction of the analyte to produce aresponse at the electrode, or both. In some embodiments, the sensinglayer has a generally dry or non-hydrated state prior to use. In suchembodiments, the sensing layer can be hydrated during use by waterwithin the fluid sample being tested.

FIGS. 1-4 illustrate a sensor 20 having features that are examples ofinventive aspects in accordance with the principles of the presentdisclosure. The sensor 20 includes an elongated member 22 having atleast a portion that is electrically conductive and that functions as aworking electrode. The elongated member 22 can include a sensing layer24 that covers or is positioned adjacent to the working electrode. Aninsulating layer 26 surrounds the elongated member 22. The sensor 20includes a sensing tip 28 at which the insulating layer 26 does notcover/enclose the elongated member 22 (e.g., the tip of the elongatedmember 22 is exposed). This open tip configuration provides an accessopening 30 at the sensing tip 28 for allowing the material desired to besensed to enter an interior region 32 of the sensor 20. The interiorregion 32 is defined between the elongated member 22 and the insulatinglayer 26. The sensor 20 also includes a base end 29 positioned oppositefrom the sensing tip 28.

Referring to FIG. 2, the insulating layer 26 has an inner transversecross-sectional profile that is different from an outer transversecross-sectional profile of the elongated member 22. For example, in theembodiment of FIGS. 1-4, the inner transverse cross-sectional profile ofthe insulating layer 26 is generally circular, while the outertransverse cross-sectional profile of the elongated member 22 isgenerally triangular. The difference in transverse cross-sectionalprofiles between the elongated member 22 and the insulating layer 26provides channels 34 at the interior region 32 defined between theinsulating layer 26 and the elongated member 22. The channels 34 extendgenerally along the length (i.e., generally along a central longitudinalaxis 36 of the sensor 20) of the elongated member 22 and are sized toallow the material desired to be sensed to move through the interiorregion 32 along the length of the sensor 20. In other embodiments, theshapes could be reversed such that the cross-sectional profile of theinsulating layer is generally triangular and the cross-sectional profileof the elongated member is generally circular. In other embodiments,other cross-sectional profile shapes (e.g., other multi-sided shapessuch as squares, rectangles, pentagons, octagons, etc.) could be used.

FIG. 5 illustrates an electrochemical sensing system 40 thatincorporates the sensor 20 of FIGS. 1-4. The working electrode of theelongated member 22 is electrically connected to a wire 41 by aconnector or hub 42 positioned at the base end 29 of the sensor 20. Thewire 41 electrically connects the working electrode of the elongatedmember 22 to a controller 46. The controller 46 can be any type ofcontroller such as a micro-controller, a mechanical controller, asoftware driven controller, a hardware driven controller, a firmwaredriven controller, etc. The controller can include a microprocessor thatinterfaces with memory. The controller 46 is also electrically connectedto a counter electrode 48. In one embodiment, the counter electrode isonly a counter electrode. In other embodiments, the counter electrode 48can function as a counter/reference electrode and can include a layer ofsilver silver-chloride.

In use of the sensing system 40, the sensing tip 28 of the sensor 20 isimmersed within a test volume 50 of a liquid sample (e.g., a bloodsample) containing an analyte desired to be sensed. The sample may be anex vivo or in vivo sample. The test volume 50 is the volume from whichthe analyte desired to be sensed can diffuse into the sensor 20 duringthe sensing period. With the sensor 20 so positioned, the liquid sampleenters the channels 34 through the sensing tip 28 and can move along thelengths of the channels 34 (e.g., by capillary action) in a directionfrom the sensing tip 28 toward the base end 29. Water within the testvolume 50 can diffuse into the sensing layer 24 such that the sensinglayer 24 is hydrated. The analyte within the test volume 50 alsodiffuses into the sensing layer 24. A voltage potential is then appliedbetween the counter electrode 48 and the working electrode. When thepotential is applied, an electrical current will flow through the testvolume 50 between the counter electrode 48 and the working electrode.The current is a result of the oxidation or reduction of the analyte inthe test volume 50. This electrochemical reaction occurs via theelectron transfer agent in the sensing layer 24 and the optionalelectron transfer catalyst/enzyme in the sensing layer 24. By measuringthe current flow generated at a given potential, the concentration of agiven analyte in the test sample can be determined. Those skilled in theart will recognize that current measurements can be obtained by avariety of techniques including, among other things, coulometric,potentiometric, amperometric, voltammetric, and other electrochemicaltechniques.

When the voltage potential is applied between the working and counterelectrodes, the analyte within the interior region 32 reacts with thesensing layer 24 and is consumed. Thereafter, additional analyte fromthe test volume 50 diffuses into the interior region 32 through the opensensing tip 28. As the analyte enters the interior region 32, theanalyte reacts with the portion of the sensing layer 24 located closestto the sensing tip 28 and is consumed before the analyte can migratefurther into the sensor along the channels 34. In this way, the open tipconfiguration of the insulating layer 26 extends sensor life by limitingthe amount of the sensor layer 24 that is exposed to the analyte at agiven moment in time. Over time, the portion of the sensing layer 24that is closest to the sensing tip 28 is depleted. When this occurs, theanalyte is able to move further along the channels 32 (i.e., deeper intothe sensor) to reach an active portion of the sensor layer 24. Thisprocess continues until the analyte depletes the sensing layer 24 alongthe entire lengths of the channels 34 and the life of the sensor ends.In this progression, the portion of the sensing layer 24 located at thedeepest portion of the sensor (i.e., the interior region 32 closest tothe base end 29) is the last portion of the sensing layer 24 to bedepleted.

To oxidize or reduce the analyte, a potential (versus a referencepotential) is applied across the working and counter electrodes. Theminimum magnitude of the applied potential is often dependent on theparticular electron transfer agent, analyte (if the analyte is directlyoxidized or reduced at the electrode), or second compound (if a secondcompound, such as oxygen or hydrogen peroxide, whose level is dependenton the analyte level, is directly oxidized or reduced at the electrode).The applied potential usually equals or is more oxidizing or reducing,depending on the desired electrochemical reaction, than the redoxpotential of the electron transfer agent, analyte, or second compound,whichever is directly oxidized or reduced at the electrode. Thepotential at the working electrode is typically large enough to drivethe electrochemical reaction to or near completion. When a potential isapplied between the working electrode and the counter electrode, anelectrical current will flow. The current is a result of the reductionor oxidation of the analyte or a second compound whose level is affectedby the analyte. In one embodiment, the electrochemical reaction occursvia an electron transfer agent and the optional catalyst.

In certain embodiments, the elongated member 22 of the sensor 20 caninclude an electrically conductive wire or fiber. For example, theelongated member 22 can include a metal wire or a glassy carbon fiber.In a preferred embodiment shown at FIG. 4, the elongated member 22 has acomposite structure and includes a fiber having a dielectric core 60surrounded by a conductive layer 62 which forms the working electrode ofthe sensor 20. A preferred composite fiber is sold under the nameResistat® by Shakespeare Conductive Fibers LLC. This composite fiberincludes a composite nylon monofilament conductive thread material madeconductive by the suffusion of about a 1 micron layer of carbonizednylon isomer onto a dielectric nylon core material. The Resistat®material is comprised of isomers of nylon to create the basic 2 layercomposite thread. However, many other polymers are available for theconstruction such as: polyethylene terephthalate, nylon 6, nylon 6,6,cellulose, polypropylene cellulose acetate, polyacrylonitrile andcopolymers of polyacrylonitrile for a first component and polymers suchas of polyethylene terephthalate, nylon 6, nylon 6,6, cellulose,polypropylene cellulose acetate, polyacrylonitrile and copolymers ofpolyacrylonitrile as constituents of a second component. Inherentlyconductive polymers (ICP) such as doped polyanaline or polypyrolle canbe incorporated into the conductive layer along with the carbon tocomplete the formulation. In certain embodiments, the ICP can be used asthe electrode surface alone or in conjunction with carbon. The Resistat®fiber product is currently sold with a circular transversecross-sectional profile. By post forming or extruding the Resistat®fiber, other transverse cross-sectional profiles (e.g., generallytriangular) can be provided. The Resistat® fiber is availability indiameters of 0.0025 to 0.016 inches, which as suitable for sensors inaccordance with the principles of the present disclosure. Examplepatents disclosing composite fibers suitable for use in practicingsensors in accordance with the principles of the present disclosureinclude U.S. Pat. Nos. 3,823,035; 4,255,487; 4,545,835 and 4,704,311,which are hereby incorporated by reference.

The sensing layer 24 preferably includes a sensing chemistry such as aredox compound or mediator. The term redox compound is used herein tomean a compound that can be oxidized or reduced. Exemplary redoxcompounds include transition metal complexes with organic ligands.Preferred redox compounds/mediators are osmium transition metalcomplexes with one or more ligands having a nitrogen containingheterocycle such as 2,2′-bipyridine. The sensing material can alsoinclude a redox enzyme. A redox enzyme is an enzyme that catalyzes anoxidation or reduction of an analyte. For example, a glucose oxidase orglucose dehydrogenase can be used when the analyte is glucose. Also, alactate oxidase or lactate dehydrogenase fills this role when theanalyte is lactate. In systems such as the one being described, theseenzymes catalyze the electrolysis of an analyte by transferringelectrons between the analyte and the electrode via the redox compound.Further information regarding sensing chemistry can be found at U.S.Pat. Nos. 5,264,105; 5,356,786; 5,262,035; and 5,320,725, which werepreviously incorporated by reference in their entireties.

The insulating layer 26 of the sensor 20 preferably serves numerousfunctions to the sensor 20. For example, the insulating layer 26preferably electrically insulates the elongated member 22. Additionally,the insulating layer 26 preferably provides mechanical strength forprotecting the elongated member 22. Also, as described above, theinsulating layer 26 preferably forms a barrier about the elongatedmember 22 that prevents the uncontrolled transport of a substancedesired to be sensed (e.g., an analyte such as glucose or lactate) tothe sensing layer 24. In one nonlimiting embodiment, the insulatinglayer 26 is made of a polymeric material such as polyimide, polyurethaneor other materials. In certain embodiments, the insulating layer 26 canhave a maximum outer dimension (e.g., an outer diameter) less than 0.02inches. In other embodiments, the channels 34 defined between theelongated member 22 and the insulating layer 26 can each have atransverse cross-sectional area less than or equal to 26,000 squaremicrons. In other embodiments, the ratio of perimeter arc section(defined by the inner diameter of the insulating layer 26) to chordlength (defined by a side of the elongated member 22) is about 1.2:1.

It will be appreciated that the sensor 20 can be used for ex vivo or invivo applications. In certain embodiments, the sensor 20 can beincorporated into a peripheral catheter to provide on-line monitoring ofbioanalytes in the same manner described in U.S. Pat. No. 6,464,849,that was previously incorporated by reference herein.

FIGS. 6 and 7 show a second electro-chemical sensor 120 having featuresthat are examples of inventive aspects in accordance with the principlesof the present disclosure. The sensor 120 has the same configuration asthe sensor of FIGS. 1-4, except a counter electrode 148 has beenprovided at the outer surface of the insulating layer 26. It will beappreciated that the counter electrode can only function as a counterelectrode, or could also function as a counter/reference electrode. Thecounter electrode 148 is made of an electrically conductive materialcoated or otherwise provided about the exterior of the insulation layer26. In the case where the counter electrode functions as a counterreference electrode, the electrode 148 is formed by depositing silversilver-chloride about the exterior of the insulating layer 26.

FIG. 8 shows an electrical sensing system 140 that incorporates thesensor 120 of FIGS. 6 and 7. The working electrode of the sensor 120 iselectrically connected to a wire 141 by a hub 142 positioned at a baseend of the sensor 120. The wire 141 electrically connects the workingelectrode of the sensor 120 to a controller 146. The hub 142 alsoelectrically connects the counter electrode 148 to a wire 143 thatelectrically connects the counter electrode 148 to the controller 146.As shown at FIG. 8, the open sensing tip of the sensor 120 is shownwithin a test sample 50.

FIGS. 9-11 show a third electro-chemical sensor 220 having features thatare examples of inventive aspects in accordance with the principles ofthe present disclosure. The sensor 220 has the same construction as thesensor 20 of FIGS. 1-4, except a stop arrangement 210 has been providedwithin the interior region 32 to limit the distance the sample fluid canmove along the length of the sensor 220. The stop arrangement 210includes blocking portions 211 that fill the channels 34 at a desiredlocation so that sample fluid flow is prevented from moving past thestop arrangement 210. As shown in FIG. 10, the stop arrangement 210prevents the test fluid from flowing within the channels 34 for adistance greater than a length L. In one embodiment, the blockingelements 211 are made of a material such as polytetrafluoroethylene thatallows air to pass through the stop arrangement but does not allow fluidto pass through the stop arrangement.

FIGS. 12-14 show a fourth sensor 320 having features that are examplesof inventive aspects in accordance with the principles of the presentdisclosure. The sensor 320 has the same construction as the sensor 20 ofFIGS. 1-4, except a crimp 310 has been provided around the exterior ofthe sensor 320 to limit the length L that a fluid desired to be testedcan flow into the sensor 320. The crimp 310 causes the insulating layer26 to be compressed against the elongated member 22 thereby closing thechannels 34 at the crimp location 310. Air holes can be formed throughthe insulating layer 26 adjacent the crimp location 310 to allow air toexit the channels 34 when the channels 34 are being filled with testfluid. It will be appreciated that the holes are preferably small enoughto prevent the passage of the sample fluid therethrough.

FIGS. 15-17 show a fifth sensor 420 having features that are examples ofinventive aspects in accordance with the principles of the presentdisclosure. The sensor 420 has the same general configuration as thesensor 120 of FIGS. 6 and 7, except the insulating layer 26 isintegrally formed with a connector hub 414. The connector hub 414 has anopening 415 that is coaxially aligned with the inner diameter of theinsulating layer 26. One end 417 of the opening 414 is tapered tofacilitate inserting the elongated member 22 into the insulating layer26. The connector hub 414 also includes integral stops 416 that fitwithin the channels 34 and function to prevent a sample fluid frommoving within the sensor 420 a distance greater than L. As shown at FIG.15, a controller is electrically connected to the counter and workingelectrodes through the connector hub 414.

FIG. 18 shows a sixth sensor 520 having features that are examples ofinventive aspects in accordance with the principles of the presentdisclosure. The sensor 620 has the same configuration as the sensor 120of FIGS. 6 and 7, except the working electrode has been split into threeseparate working electrodes 121 a, 121 b, 121 c each corresponding to aseparate channel of the sensor 520. Each of the working electrodes isprovided on one side of the elongated member 22 and each workingelectrode is separately connected to the controller. The controller isalso electrically connected to an integral counter electrode 148provided about the insulating layer 26. The separate working electrodescan be used to detect different types of substances/materials and can becoated with the appropriate sensing layers 124 a, 124 b, 124 c. Forexample, the working electrodes could be used to detect oxygen levels,lactate levels, glucose levels, catecholine levels or other materiallevels in a test sample and can be coated with sensing layers suitablefor detecting these materials. In still other embodiments, one of theworking electrodes could be used as a temperature sensor.

To manufacture sensors in accordance with the principles of the presentdisclosure, a conductive fiber (e.g., a Resistat® conductive fiber) isextruded or post-formed to have a desired cross sectional profile (e.g.,triangular). As used herein, the term fiber includes threads, filaments,monofilaments, and other like elongated structures. The surface of thefiber is then cleaned (e.g., with an ultrasonic cleaner or degreaser),rinsed and dried. The surface can then be treated to improve itshydrophilic properties and/or can be activated with a plasma.Thereafter, the shaped fiber is passed through sequential coatingstations by means of a reel to reel continuous process. At each stationsuccessive layers of sensor chemistry are applied uniformly as thinfilms and cured prior to entering the next station. The processed fiberis collected on storage reels for use in the succeeding step. Estimatedprocess time is ˜20 feet per minute yielding ˜24,000 sub-componentfibers per hour.

The cured length of fiber is collected on reels then supplied as feedstock to an assembly process where the fiber is first caused to enter asmall thermoplastic molded hub (e.g., connector hub 414 of FIG. 15)having a tapered opening on one end capable of guiding the fiberpreferably into an integral polyimide tube that is fixed to the opposingface of the fiber entry point and that forms the insulating layer of thesensor. The exterior of the tube 26 may be coated by various means withAg/AgCl in order to provide an integral reference electrode 148 inconcert with the working electrode of the internal fiber. In certainembodiments, the Ag/AgCl can be coated directly, or the part can becoated with Ag and then converted to an Ag/AgCl coating by oxidation ofthe Ag in a high Cl containing electrolyte. The connector hub can besecured to the fiber by means of sonic or induction weld to the fiber.The connector hub can include electrical connections to the working andcounter electrodes and can include contact points on the connector hubthat will later provide interconnection to a transmitter or output wiresaccording to the application requirement in concert with contacts fromthe reference electrode. Finally, the fiber is cut to length in placewithin the insulator tube 26.

Suitable fixtures and “Pick and place” robotics can be used tointermittently feed the fiber into the short (e.g., 10 millimeter) huband tube component, perform the cutting operation and place thecompleted sensor into carrier pallets for final assembly and packaging.

The various aspects disclosed herein provide numerous advantages. Forexample, the use of a chemically coated fiber covered by a separateinsulator tube that is not adhered to the fiber allows for bothstructural enhancement and additional design flexibility. Also, the useof composite fiber as compared to pure glassy carbon fibers improvessensor durability and flexibility. Further, by using channels definedbetween the elongated member and the insulating layer, rapid hydrationis possible thereby reducing the time required to activate the sensor.Further, the use of a fiber with an inert/dielectric core assists inblocking potential signal interference that might otherwise occur at theend of the fiber. Moreover, the cross sectional shape of thefiber/insulator interface profile is preferably not concentric but is ofdiffering geometry, typically having multiple sides separated by angles(e.g., triangular, square, rectangular, pentagonal, hexagonal, etc).This configuration provides distinct multiple ports or channels whichallow for providing different working electrodes associated with eachport or channel. Using angular shaped fibers also provides limitedpoints of contact around the insulator tube interior that both locatethe fiber centrally within the tube—thus defining the port openings, aswell as create minimal frictional contact between tube and fiber forease of making a telescoping assembly of the two components. Limitedpoint contacts also act as to prevent damage to the fragile chemistrycoating from sliding surfaces between the fiber and the inner tube wallwhen mated in this fashion. The limited contact points also protect thesensor chemistry after assembly. For example, when the sensor is bentcausing relative axial movement between the insulating layer and theconductive fiber, only the corners are subject to friction between theinsulating layer and the fiber.

From the foregoing detailed description, it will be evident thatmodifications and variations can be made without departing from thespirit or scope of the broad inventive aspects embodied in theembodiments disclosed herein. For example, any of the embodimentsdisclosed herein can use separate reference and counter electrodesinstead of combined counter/reference electrodes.

1-30. (canceled)
 31. A sensor comprising: an elongated member includinga dielectric core surrounded at least partially by an electricallyconductive layer that forms a working electrode; a sensing chemistrypositioned adjacent to the electrically conductive layer; an insulatinglayer at least partially enclosing the elongated member and the sensingchemistry; and channels defined between the insulating layer and thesensing chemistry, the channels extending at least partially along alength of the elongated member.
 32. The sensor of claim 31, wherein theelongated member has a diameter less than 0.02 inches.
 33. The sensor ofclaim 31, wherein the elongated member includes a fiber.
 34. The sensorof claim 33, wherein the fiber includes a composite monofilament threadmaterial made conductive by a suffusion of the conductive layer on thedielectric core.
 35. The sensor of claim 31, wherein the sensingchemistry includes a redox compound.
 36. The sensor of claim 35, whereinthe redox compound includes a transition metal complex with an organicligand.
 37. The sensor of claim 35, wherein the sensing chemistryincludes a redox enzyme.
 38. The sensor of claim 37, wherein the redoxenzyme includes glucose oxidase, glucose dehydrogenase, lactate oxidase,or lactate dehydrogenase.
 39. The sensor of claim 31, wherein thesensing chemistry includes a sensing layer that covers at least aportion of the conductive layer.
 40. The sensor of claim 31, wherein thesensor includes a sensing tip defining an opening in the insulatinglayer for allowing a material to be analyzed to enter an interior of theinsulating layer.
 41. The sensor of claim 31, wherein the insulatinglayer defines an opening for allowing a material to be analyzed to reachthe sensing layer.
 42. The sensor of claim 31, further comprising acounter electrode carried by the insulating layer.
 43. The sensor ofclaim 31, wherein the insulating layer has an inner cross-sectionalshape that is different from an outer cross-sectional shape of theelongated member.
 44. The sensor of claim 43, wherein the innercross-sectional shape of the insulating layer is circular and the outercross-sectional shape of the elongated member is triangular.
 45. Thesensor of claim 31, wherein first and second separate working electrodesare provided on the elongated member.
 46. The sensor of claim 45,wherein first and second different sensing chemistries are provided onthe first and second working electrodes.
 47. The sensor of claim 45,wherein the elongated member includes a plurality of discrete sides,wherein the plurality of discrete sides include at least first andsecond sides, and wherein the first working electrode is positioned atthe first side and the second working electrode is positioned at thesecond side.
 48. A sensor comprising: an elongated member including atleast a portion that is electrically conductive, the elongated memberincluding a sensing material adapted to react with a material to beanalyzed; and an insulating layer that surrounds the elongated member,the insulating layer defining at least one access opening for allowingthe material to analyzed to enter an interior region defined between theelongated member and the insulating layer, the insulating layer havingan inner transverse cross-sectional profile that is different from anouter transverse cross-sectional profile of the elongated member, thedifference in transverse cross-sectional profiles between the elongatedmember and the insulating layer providing channels at the interiorregion defined between the insulating layer and the elongated member,the channels extending generally along a length of the elongated member.49. The sensor of claim 48, further comprising a stop arrangement forlimiting a distance a sample fluid can flow along lengths of thechannels.
 50. The sensor of claim 48, wherein the sensing material isconfigured to be hydrated by the analyte as the analyte diffuses intothe sensing layer along a length of the channels.